Major geomagnetic storms represent a signiΓΏcant dissipation of energy by the magnetosphere. The energy is derived from the solar wind ow and the subsequent powerful conversion of that energy takes several di erent forms. Ring current injection and decay, ionospheric Joule heating, particle precipitation into the atmosphere, and several related physical processes are exhibited clearly in large storm events. The modern-day constellation of operating spacecraft gives an unprecedented opportunity to study magnetic storm processes and energetics. This paper focuses on recent coronal mass ejection (CME) events that have been well-observed near the sun. These disturbances are followed from the sun to their arrival in near-Earth space. The reconΓΏguration of the magnetosphere under the driving in uence of CME=magnetic cloud events is examined and the energetics of various forms of input and output are assessed. It is concluded that the present observations in the ISTP era, along with modern modeling techniques, have given us new insights into geomagnetic stormtime energy dissipation. Ionospheric Joule heating and auroral particle precipitation account for a substantial majority of energy dissipation during CME-driven storms (i.e., &70%). However, ring current energy injection due to moderate energy ions is also a key. Direct in situ observations of such ions are found to be crucially important because indices such as Dst may be contaminated by many other e ects.